Oxidation of 2,3,6-trimethylphenol in the Presence of Molybdovanadophosphoric Heteropoly Acids
Journal of Molecular Catalysis (Continued after 1994 as Journal of Molecular Catalysis A: Chemical and Journal of Molecular Catalysis B: Enzymatic)
Oxidation of 2,3,6-trimethylphenol (TMP) by O2 in the presence of heteropoly acids H3+nPMo12−nVnO40 (HPA-n) in AcOHH2O gives up to 86% 2,3,5-trimethyl-1,4-benzoquinone (TMBQ) at a 100% TMP conversion, 2,2′,3,3′,6,6′-hexamethyl-4,4′-biphenol (BP) also being formed. The yield of BP increases at the expense of TMBQ with increasing H2O content. BP was shown to be an intermediate in TMP oxidation to TMBQ. Evidence is provided that the catalytically active species is the VO2+ ion formed via dissociation of HPA-n. A stepwise mechanism including the oxidation of TMP by V(V) to produce TMBQ and V(IV) followed by oxidation of V(IV) to V(V) with dioxygen in the coordination sphere of the heteropoly anion is suggested.